1. Field of the Invention
The present invention relates generally to optical communications systems, and more particularly to a subsystem for routing wavelengths in an optical communications system through use of slidable two-section channel filters allowing direction of a selected wavelength without interrupting express channels.
2. Brief Description of the Prior Art
Optical communications networks are capable of handling large quantities of data due to their very broad bandwidth. This capability is enhanced through the simultaneous transmission of a plurality of carriers of different wavelengths. A technique known as wavelength division multiplexing is used to place the various carriers on a single optic network and separate the wavelengths at a node for re-routing. A system/module for use in receiving and/or transmitting a selected carrier wavelength at a node in an optical communications system is described in U.S. Pat. No. 5,712,932 by Alexander et al. This system uses circulators and a series of fixed tuned Bragg filters that are switched in or out of the network to receive (drop) or add (transmit) a particular carrier wavelength. A disadvantage of this is that the flow of express channels/wavelengths is disturbed during the switching moments, a problem that can cause a loss of data. A system that avoids the use of switches is described in U.S. Pat. No. 5,706,375 by Mihailov et al. wherein a specific wavelength is selected by tuning a Bragg filter in and out of a corresponding channel. A disadvantage of this system is the complexity and cost of the tuning mechanism.
In view of the prior art discussed above, it is apparent that a need exists for an improved optical add/drop module/system that is amenable to low cost and reliable construction.
It is therefore an object of the present invention to provide an improved add/drop system for use in an optical communications network.
It is a further object of the present invention to provide an add/drop module that does not disturb the flow of express channels during an add/drop procedure.
It is another object of the present invention to provide an add/drop module that avoids the use of costly Bragg filters.
Briefly, a preferred embodiment of the present invention includes an add/drop module system for use in routing carrier wavelengths through an optical communications network. The system includes a first network interface GRIN lens collimator connected on one end to an optical fiber of a communications network. An output of the GRIN lens is directed to a series of slidable two-section channel filters. Each filter is mechanically movable to a first position that passes all wavelengths. Electrical relays slide the filters from the first position to a second position upon input of a directive signal. The second position of each filter reflects a particular wavelength to a corresponding add/drop GRIN lens collimator that receives the reflected light wavelength and outputs it into an add/drop optical fiber. The outputs from the add/drop collimators are directed to a single add/drop optical fiber through use of a power combiner. Light that passes through all of the filters is directed into a second network interface GRIN lens collimator for the purpose of coupling the light onto a second network optical fiber. Optical carriers arriving on the first network fiber can therefore either be dropped to the add/drop port or passed through for transmission on the second fiber. A carrier wavelength can also be entered added at the add/drop port. In order for an added wavelength to be added to the network, it must correspond to a wavelength of one of the filters, which must be positioned to reflect the signal. With the filter in this position, the added wavelength is reflected and passed to the first GRIN lens collimator which couples the signal onto the first network fiber.